Effects of feedstock and co-culture of Lactobacillus fermentum and wild Saccharomyces cerevisiae strain during fuel ethanol fermentation by the industrial yeast strain PE-2

Abstract

Even though contamination by bacteria and wild yeasts are frequently observed during fuel ethanol fermentation, our knowledge regarding the effects of both contaminants together is very limited, especially considering that the must composition can vary from exclusively sugarcane juice to a mixture of molasses and juice, affecting the microbial development. Here we studied the effects of the feedstock (sugarcane juice and molasses) and the co-culture of Lactobacillus fermentum and a wild Saccharomyces cerevisiae strain (rough colony and pseudohyphae) in single and multiple-batch fermentation trials with an industrial strain of S. cerevisiae (PE-2) as starter yeast. The results indicate that in multiple-cycle batch system, the feedstock had a minor impact on the fermentation than in single-cycle batch system, however the rough yeast contamination was more harmful than the bacterial contamination in multiple-cycle batch fermentation. The inoculation of both contaminants did not potentiate the detrimental effect in any substrate. The residual sugar concentration in the fermented broth had a higher concentration of fructose than glucose for all fermentations, but in the presence of the rough yeast, the discrepancy between fructose and glucose concentrations were markedly higher, especially in molasses. The biggest problem associated with incomplete fermentation seemed to be the lower consumption rate of sugar and the reduced fructose preference of the rough yeast rather than the lower invertase activity. Lower ethanol production, acetate production and higher residual sugar concentration are characteristics strongly associated with the rough yeast strain and they were not potentiated with the inoculation of L. fermentum.

A Novel Cold-Adaptive Endo-1,4-β-Glucanase From Burkholderia pyrrocinia JK-SH007: Gene Expression and Characterization of the Enzyme and Mode of Action

“…Conversion of cellulose to bioethanol is a two-step process: saccharification and fermentation, respectively. The saccharification process is conducted at higher temperatures between 50 and 55 • C (which requires high energy and cost) (Murashima et al, 2002;Wang et al, 2009;Liu et al, 2016), while the ethanol fermentation using Saccharomyces cerevisiae occurs at lower temperatures between 25 and 30 • C (Borrull et al, 2016;Reis et al, 2018). Thus a cold-adaptive, endo-β-1,4-glucanase catalyzing the saccharification process under ambient temperatures could be of high significance.…”

Automatic cell segmentation from brightfield microscopy images of pseudohyphal cell-aggregates

“…This biotype of cell yeast morphology is also called snowflake [6]. Studies have shown that a wild S. cerevisiae strain exhibiting pseudohyphal morphology is often associated with lower ethanol production and higher residual sugar content in the fermented must [7,8]. In contrast, in the brewing and chemical manufacturing industry, pseudohyphal yeasts have been exploited to change flavour and aroma in beverage products and to produce acetic acid, respectively [9].…”

“…The strain (originally termed 'strain 52') was identified by the sequencing of the D1/D2 region of the large subunit (26S) rRNA and deposited at the culture collection 'Coleção de Culturas Tropical' of 'Fundação André Tosello', Campinas-SP-Brazil under the code CCT7787. This yeast strain was utilized in previous studies of fermentation characteristics[5,7,8].…”

Metabólitos excretados na fermentação alcoólica como possíveis substratos para o crescimento do gênero <i>Lactobacillus</i>

“…A presença das bactérias contaminantes na dorna afeta o desempenho da cepa de levedura durante a fermentação industrial (BECKNER et al, CHANG et al, 1995;JOUHTEN et al, 2016;NARENDRANATH et al, 1997;REIS et al, 2018). Dentre os fatores estão, a produção de ácido lático e acético que diminuem o pH do meio e ainda, quando na forma não dissociada, os ácidos orgânicos difundem pela membrana celular ao meio intracelular, acidificando o citoplasma com a liberação de íons H + (BASSO et al, 2014;BECKNER et al, 2011;NARENDRANATH et al, 2001;REIS et al, 2018;THOMAS et al 2001 BECKNER et al, 2011).…”

“…Durante a fermentação, os microrganismos contaminantes interagem de forma negativa com a cepa de levedura (BECKNER et al, 2011) em que as bactérias homo e heterofermentativas afetam de maneira distinta sua viabilidade e desempenho fermentativo (BASSO et al, 2014). Dentre os mecanismos envolvidos na interação, têm-se a produção pelas LAB de ácidos orgânicos e outros metabólitos (BECKNER et al, 2011;REIS et al, 2018), competição por substrato (LEROI e PIDOUX, 1993) e nutrientes (BAYROCK e INGLEDEW, 2004). Além disso, as bactérias ocasionam a floculação celular da levedura em decorrência da presença da manose em sua parede celular, fazendo com que ocorra a aglutinação entre as células e biofilme bacteriano, afetando a eficiência fermentativa da levedura (PRETZER et al, 2005).…”